150 research outputs found
Extreme Energy Cosmic Rays: Bottom-up vs. Top-down scenarii
We present an overview on extreme energy cosmic rays (EECR) and the
fundamental physics connected with them. The top-down and bottom-up scenarii
are contrasted. We summarize the essential features underlying the top-down
scenarii for EECR, namely, the lifetime and the mass {\bf imposed} to the heavy
relics whatever they be: topological and non-topological solitons, X-particles,
cosmic defects, microscopic black-holes, fundamental strings. An unified
formula for the quantum decay rate of all these objects was provided in
hep-ph/0202249. The key point in the top-down scenarii is the necessity to {\bf
adjust} the lifetime of the heavy object to the age of the universe. The
natural lifetimes of such heavy objects are, however, microscopic times
associated to the GUT energy scale (sim 10^{-28} sec. or shorter); such heavy
objects could have been abundantly formed by the end of inflation and it seems
natural they decayed shortly after being formed. The arguments produced to {\bf
fine tune} the relics lifetime to the age of the universe are critically
analyzed. The annihilation scenario (`Wimpzillas') is analyzed too. Top-down
scenarii based on networks of topological defects are strongly disfavored at
the light of the recent CMB anisotropy observations. We discuss the
acceleration mechanisms of cosmic rays,their possible astrophysical sources and
the main open physical problems and difficulties in the context of bottom-up
scenarii, and we conclude by outlining the expectations from future
observatories like EUSO and where the theoretical effort should be placed.Comment: LaTex, 16 pages, 2 .eps figures. The annihilation scenario
(Wimpzillas) is included and the discussion on gamma ray bursts improved.
Based on lectures at the Fourth International Workshop on `New Worlds in
Astroparticle Physics' in Faro, Portugal, September 2002, at the 9th Course
on Astrofundamental Physics of the Chalonge School, Palermo, Italia,
September 2002 and at the SOWG EUSO meeting, Roma, Italia, November 200
Skyrmion Multi-Walls
Skyrmion walls are topologically-nontrivial solutions of the Skyrme system
which are periodic in two spatial directions. We report numerical
investigations which show that solutions representing parallel multi-walls
exist. The most stable configuration is that of the square -wall, which in
the limit becomes the cubically-symmetric Skyrme crystal. There is
also a solution resembling parallel hexagonal walls, but this is less stable.Comment: 7 pages, 1 figur
Fair scans of the seesaw. Consequences for predictions on LFV processes
Usual analyses based on scans of the seesaw parameter-space can be biassed
since they do not cover in a fair way the complete parameter-space. More
precisely, we show that in the common "R-parametrization", many acceptable
R-matrices, compatible with the perturbativity of Yukawa couplings, are
normally disregarded from the beginning, which produces biasses in the results.
We give a straightforward procedure to scan the space of complex R-matrices in
a complete way, giving a very simple rule to incorporate the perturbativity
requirement as a condition for the entries of the R-matrix, something not
considered before. As a relevant application of this, we show that the extended
believe that BR(mu --> e, gamma) in supersymmetric seesaw models depends
strongly on the value of theta_13 is an "optical effect" produced by such
biassed scans, and does not hold after a careful analytical and numerical
study. When the complete scan is done, BR(mu --> e, gamma) gets very
insensitive to theta_13. Moreover, the values of the branching ratio are
typically larger than those quoted in the literature, due to the large number
of acceptable points in the parameter-space which were not considered before.
Including (unflavoured) leptogenesis does not introduce any further dependence
on theta_13, although decreases the typical value of BR(mu --> e, gamma).Comment: 22 pages, 5 figure
New Solution for Neutrino Masses and Leptogenesis in Adjoint SU(5)
We investigate baryogenesis via leptogenesis and generation of neutrino
masses and mixings through the Type I plus Type III seesaw plus an one-loop
mechanism in the context of Renormalizable Adjoint SU(5) theory. One light
neutrino remains massless, because the contributions of three heavy Majorana
fermions \rho_0, \rho_3 and \rho_8 to the neutrino mass matrix are not linearly
independent. However none of these heavy fermions is decoupled from the
generation of neutrino masses. This opens a new range in parameter space for
successful leptogenesis, in particular, allows for inverted hierarchy of the
neutrino masses.Comment: 16 pages, 4 figures; references added and typos fixe
The Sphaleron Rate in SU(N) Gauge Theory
The sphaleron rate is defined as the diffusion constant for topological
number NCS = int g^2 F Fdual/32 pi^2. It establishes the rate of equilibration
of axial light quark number in QCD and is of interest both in electroweak
baryogenesis and possibly in heavy ion collisions. We calculate the
weak-coupling behavior of the SU(3) sphaleron rate, as well as making the most
sensible extrapolation towards intermediate coupling which we can. We also
study the behavior of the sphaleron rate at weak coupling at large Nc.Comment: 18 pages with 3 figure
Sphalerons and the Electroweak Phase Transition in Models with Higher Scalar Representations
In this work we investigate the sphaleron solution in a
gauge theory, which also encompasses the Standard Model, with higher scalar
representation(s) (). We show that the field profiles
describing the sphaleron in higher scalar multiplet, have similar trends like
the doublet case with respect to the radial distance. We compute the sphaleron
energy and find that it scales linearly with the vacuum expectation value of
the scalar field and its slope depends on the representation. We also
investigate the effect of gauge field and find that it is small for the
physical value of the mixing angle, and resembles the case for the
doublet. For higher representations, we show that the criterion for strong
first order phase transition, , is relaxed with respect to
the doublet case, i.e. .Comment: 20 pages, 5 figures & 1 table, published versio
Aidnogenesis via Leptogenesis and Dark Sphalerons
We discuss aidnogenesis, the generation of a dark matter asymmetry via new
sphaleron processes associated to an extra non-abelian gauge symmetry common to
both the visible and the dark sectors. Such a theory can naturally produce an
abundance of asymmetric dark matter which is of the same size as the lepton and
baryon asymmetries, as suggested by the similar sizes of the observed baryonic
and dark matter energy content, and provide a definite prediction for the mass
of the dark matter particle. We discuss in detail a minimal realization in
which the Standard Model is only extended by dark matter fermions which form
"dark baryons" through an SU(3) interaction, and a (broken) horizontal symmetry
that induces the new sphalerons. The dark matter mass is predicted to be
approximately 6 GeV, close to the region favored by DAMA and CoGeNT.
Furthermore, a remnant of the horizontal symmetry should be broken at a lower
scale and can also explain the Tevatron dimuon anomaly.Comment: Minor changes, discussion of present constraints expanded. 16 pages,
2 eps figures, REVTeX
Implications of Flavor Dynamics for Fermion Triplet Leptogenesis
We analyze the importance of flavor effects in models in which leptogenesis
proceeds via the decay of Majorana electroweak triplets. We find that depending
on the relative strengths of gauge and Yukawa reactions the asymmetry can
be sizably enhanced, exceeding in some cases an order of magnitude level. We
also discuss the impact that such effects can have for TeV-scale triplets
showing that as long as the asymmetry is produced by the dynamics of the
lightest such triplet they are negligible, but open the possibility for
scenarios in which the asymmetry is generated above the TeV scale by heavier
states, possibly surviving the TeV triplet related washouts. We investigate
these cases and show how they can be disentangled at the LHC by using Majorana
triplet collider observables and, in the case of minimal type III see-saw
models even through lepton flavor violation observables.Comment: 22 pages, 9 figures, extended discussion on collider phenomenology,
references added. Version matches publication in JHE
- …